Soft Nanoparticles Assembled from Linear Poly(ethylene glycol) and Linear Brush Polydimethylsiloxane Diblock Copolymers Andri Halim, 1,2 Timothy D. Reid, 2 Jing M. Ren, 2 Qiang Fu, 1,2 Paul A. Gurr, 1,2 Anton Blencowe, 2 * Sandra E. Kentish, 1 Greg G. Qiao 1,2 1 Department of Chemical and Biomolecular Engineering, Cooperative Research Centre for Greenhouse Gas Technologies, University of Melbourne, Parkville, Victoria 3010, Australia 2 Department of Chemical and Biomolecular Engineering, Polymer Science Group, University of Melbourne, Parkville, Victoria 3010, Australia Correspondence to: G. G. Qiao (E - mail: gregghq@unimelb.edu.au) Received 1 November 2013; accepted 21 December 2013; published online 18 February 2014 DOI: 10.1002/pola.27111 ABSTRACT: A series of novel amphiphilic diblock copolymers composed of hydrophilic linear poly(ethylene glycol) (PEG) and linear brush hydrophobic polydimethylsiloxane (PDMS) were synthesized. Three different molecular weights of monomethyl ether PEG were initially functionalized with 2-bromoisobutyryl bromide to afford macroinitiators suitable for atom-transfer radical polymerization. The macroinitiators were characterized by gel permeation chromatography, 1 H and 13 C nuclear mag- netic resonance spectroscopic analysis and matrix-assisted laser desorption ionization time-of-flight mass spectroscopy. The three different molecular weight macroinitiators were then chain extended with monomethacryloxypropyl-terminated PDMS and photoactive 2-(methylacyloyloxy)ethyl anthracene-9- carboxylate in different molar ratios to afford a series of photo- responsive amphiphilic diblock copolymers with high conver- sions. Self-assembly of these linear–linear brush diblock copolymers in N,N-dimethylformamide afforded nanoparticles with hydrodynamic diameters (d H ) ranging from 41 to 268 nm, as determined by dynamic light scattering analysis. Crosslink- ing and stabilization of the nanoparticles was achieved via [414] photodimerization of the anthracene moieties upon exposure to UV radiation at 365 nm with the reverse reaction studied at a wavelength of 254 nm. Transmission electron microscopy revealed that the self-assembled nanoparticles and their crosslinked derivatives had spherical morphologies. VC 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1251–1262 KEYWORDS: anthracene; atom transfer radical polymerization (ATRP); block copolymers; poly(dimethylsiloxane); poly(ethyl- ene glycol); polysiloxanes; self-assembly INTRODUCTION The last decade has seen nanotechnology emerging as one of the most significant areas in research and development in both academia and industry. 1,2 “Nanoscience” has developed into a multidisciplinary field, ranging from fundamental in-depth studies to the fabrication of next-generation functional materials for a wide range of applications. “Soft” materials such as micelles and vesicles have been extensively used in the biomedical field, whereas the application of such materials to separation technologies has been less explored. 3,4 Poly(ethylene glycol) (PEG) is a water-soluble polymer that has attracted much attention as a result of its biocompatibil- ity and low toxicity. 5 PEG has been widely employed in a variety of biomedical applications including the preparation of biocompatible conjugates, surface modification of drug delivery vectors, and as scaffolds for tissue engineering. 6 PEG has also been significant in the development of mem- branes for CO 2 separation as it possesses a high affinity towards CO 2 . 7–9 Additionally, PEG is readily available, inex- pensive, and easily produced on an industrial scale. Polydi- methylsiloxane (PDMS) is a class of hydrophobic rubbery polymer that has been utilized in many areas as a result of its high stability, biocompatibility, and flexibility. 10–12 In the gas separation field, PDMS is known as one of the most per- meable polymers, which results from the flexibility of the siloxane backbone. 13–15 The formation of amphiphilic block copolymers (BCPs) can be achieved by covalently linking Additional Supporting Information may be found in the online version of this article. *Present address: Anton Blencowe, Mawson Institute, Division of Information Technology, Engineering and the Environment, Uni- versity of South Australia, South Australia 5095, Australia VC 2014 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 1251–1262 1251 JOURNAL OF POLYMER SCIENCE WWW.POLYMERCHEMISTRY.ORG ARTICLE